Gold/silver alloys

ABSTRACT

A tarnish resistant Au/Ag alloy of low gold content exhibiting properties desired in jewelry manufacture consisting essentially of about 25 to 30 percent by weight gold, about 45 to 71 percent by weight silver, about 3 to 25 percent by weight copper, and 0 to about 5 percent by weight zinc.

United States Patent Kohl-n et a]. Dec. 9, 1975 GOLD/SILVER ALLOYS [56]References Cited [76] Inventors: Edward Louis Kohrn, 9 Sunset UNITEDSTATES PATENTS Drive, Cape Arthur, Sevema Park, 1,090,939 3/1914 Newton75/173 C X Md. 21146; Seymour Globus, 268 Wakely Terrace, Bel Air, Md.Primary Examiner-L. Dewayne Rutledge 21014 Assistant ExaminerE. L. WeiseAttorney, Agent, or FirmLarson, Taylor and Hinds [22] Filed: Nov. 26,1974 2| Appl. No.: 527,139 [571 ABSTRACT A tarnish resistant Au/Ag alloyof low gold content ex- Related Apphcmlon Data hibiting propertiesdesired in jewelry manufacture [63] Continuation-impart of Ser. No480,890, June 19, Consisting essentially of about 25 to 30 percent by1974. weight gold, about 45 to 71 percent hy weight silver, about 3 to25 percent by weight copper, and O to [22] 75/173 C; 75/134 N about 5percent by weight Zinc t. CZZC 5/06 4 Claims No Drawings Field of 75/173C, I65, l34 C, 134 N GOLD/SILVER ALLOYS This application is acontinuation-in-part of parent application Ser. No. 480,890 filed June19, I974.

BACKGROUND OF THE INVENTION This invention relates to improvements ingold base alloys. More particularly the present invention is directed tolow gold alloys possessing the properties desired in the manufacture ofarticles of jewelry.

Gold, per se, being a relatively soft metal is unsuitable for themanufacture of jewelry articles and must be alloyed with other metals soas to acquire the properties that make it serviceable for jewelrypurposes. The most desirable properties for jewelry purposes in goldbase alloys are castability, workability, tarnish resistance, luster andcolor. To achieve these properties it is generally necessary for thegold content of the alloys to be at least 41 .65% by weight (i.e., atleast karat). It is well recognized that gold base alloys containinglevels of gold lower than about 4t .65% exhibit low tarnish resistanceand quite often poor castability and workability. These drawbacks whichcharacterize low gold alloys are particularly true of the gold/silveralloys of the prior art.

Attempts have been made to overcome this problem of poor tarnishresistance in below 10 karat gold/silver alloys by the inclusion in suchalloys of minor amounts of other metals. Unfortunately these effortshave not been without their shortcomings for while tarnish resistancemay be improved by such additions, one or more of the other desiredproperties, i.e. workability, castability including porosity, luster andcolor are invariably adversely effected.

OBJECTS OF THE INVENTION One object of the present invention thereforeis to provide a low gold alloy which possesses all the desiredproperties for jewelry manufacture.

Thus, it is an object of the invention to provide a low gold base alloythat can be worked, cast, molded, engraved, soldered and stamped usingexisting techniques with normal jewelry equipment.

It is also an object of the invention to provide a low gold alloy whichis of sufficient hardness to take a normal jewelry finish either brightor textured as desired.

Another object of the invention is to provide a low gold base alloycharacterized by a substantially total loss of porosity.

Yet another object of the invention is to provide a low gold base alloyof excellent color and luster.

A further object of the invention is to provide a low base alloy whichin addition to possessing the aforementioned properties manifests a hightarnish resistance under normal usage.

Another object of the present invention is to produce a low gold basealloy that is characterized by an electrical conductivity substantiallythat of pure gold.

Still another object of the invention is to provide both yellow andwhite low gold alloys which can be cold drawn to essentially the samehigh levels without substantial loss.

Lastly, it is an object of the invention to provide at substantiallyreduced cost a low gold alloy which is a substitute for and whichpossesses all the beneficial properties of 10-14 karat gold base alloys.

SUMMARY OF THE INVENTION These and other objects of the invention areobtained by a metal alloy consisting essentially of about 25 to 30percent by weight gold, about 45 to 71 percent by weight silver, about 3to 25 percent by weight copper and 0 to about 5 percent zinc.

DETAILED DESCRIPTION The color of the alloys of the invention are eitheryellow or white depending upon the concentrations of silver and copperpresent in the metal alloy. In the case of yellow alloys the metal alloyconsists essentially of about 25 to 30 percent, preferably 27 to 29percent by weight gold; about 45 to 57 percent, preferably 47 to 55percent by weight silver; about 18 to 25 percent, preferably about 18 to23 percent by weight of copper and 0 to about 5 percent, preferablyabout I to 3.5 percent by weight zinc.

Illustrative of preferred yellow alloys are those consisting essentiallyof about 25 to 30 percent by weight, gold, about 45 to 57 percent byweight, silver, about l8 to 20 percent by weight, copper and about I to3.5 percent by weight, zinc.

In the case of white alloys the metal alloy consists essentially ofabout 25 to 30 percent by weight gold; about 57 to 71 percent by weightsilver; about 3 to 10 percent by weight copper and 0 to about 5 percentby weight zinc.

Preferred white alloys consist essentially of about 25 to 30 percent byweight gold, about 65 to 68 percent by weight silver, about 3 to 5percent by weight copper and about 0 to 2 percent by weight zinc.

The process of manufacturing the alloys of the invention does not differfrom the standard practice in the manufacture of alloys of preciousmetals. The alloys may be prepared by simply weighing out the properproportions of the constituents, placing them in a re fractory crucibleand subjecting the mixture to a heat sufficient to melt the materials.Care should be taken, however, to insure uniform alloying and mixing ofthe constituents.

A more convenient method for preparing yellow gold alloys of theinvention comprises alloying in equal proportions l4 karat yellow goldwith sterling silver. The composition of 14 karat yellow gold generallyis as follows: 56.25% Au, 30.7-32.8% Cu, 4.2-l0.5% Ag and 27% Zn.Sterling silver is constituted of 92.5% Ag and 7.5% Cu. Thus, theconstituencies of these materials is such that 50/50 blends of theyellow 14 karat gold and sterling silver provides novel low yellow goldalloys of the invention. White gold alloys of the invention on the otherhand are most conveniently prepared by blending in the properproportions pure gold, pure silver, copper and optionally zinc.

The following examples are included to further illustrate the presentinvention.

EXAMPLE I A 50/50 blend of 14 karat yellow gold and sterling silver wereweighed and charged together into a refractory crucible wherein theywere heated to a temperature of 1600F with a gas torch until completelymelted. The melt was stirred with a graphite rod immediately prior tocasting and the alloy melt was then cast in air into a standardinvestment mold in the form of a ring. Upon eoolin the alloy casting wasremoved and found to Be 'sbii'ri with good surface fidelity and with-EXAMPLE II In a refractory crucible were chared 29.17% by weight puregold, 67% by weight pure silver with the balance copper. The mixture ofmetals was melted and cast as described in Example I. The resultingwhite alloy ring after the usual clean up was mechanically worked,chased and burnished as in Example The finished ring possessed the sameadvantageous properties as the yellow alloy ring of Example l.

While the features of this invention have been disclosed with referenceto the specific embodiments described therein, it is to be understoodthat various modifications may be made in the details of the manufacturewithout departing from the scope of this invention as defined in theappended claims.

It is claimed:

1. A metal alloy consisting essentially of about 25 to 30 percent byweight gold, about 57 to 71 percent by weight silver, about 3 to 10percent by weight copper and about 0 to 5 weight percent zinc.

2. A metal alloy consisting essentially of about 25 to 30 percent byweight gold, about 65 to 68 percent by weight silver, about 3 to 10percent by weight copper and about 0 to 2 percent by weight zinc.

3. An article ofjewelry formed of the alloy of claim 1.

4. An article of jewelry formed by the alloy of claim 2.

1. A METAL ALLOY CONSISTING ESSENTIALLY OF ABOUT 25 TO 30 PERCENT BYWEIGHT GOLD, ABOUT 57 TO 71 PERCENT BY WEIGHT SILVER, ABOUT 3 TO 10PERCENT BY WEIGHT COPPER AND ABOUT 0 TO 5 WEIGHT PERCENT ZINC.
 2. Ametal alloy consisting essentially of about 25 to 30 percent by weightgold, about 65 to 68 percent by weight silver, about 3 to 10 percent byweight copper and about 0 to 2 percent by weight zinc.
 3. An article ofjewelry formed of the alloy of claim
 1. 4. An article of jewelry formedby the alloy of claim 2.